1. Field of the Invention
The present invention relates to an endoscope having a flexible section, and particularly to endoscopes having flexible sections of various forms and operation forces.
2. Description of the Prior Art
FIG. 1 shows a conventional endoscope. The endoscope comprises a front end 101 having an observation window, an illumination window, a forceps mouth, etc., for observing and treating celomic sites, a flexible tube 103, a flexible section 105 disposed between the front end 101 and the flexible tube 103, and a controller 107 disposed at the other end of the flexible tube 103 to curve the flexible section 105.
The flexible section 105 comprises a plurality of articular rings that are connected to one another through joints. The articular rings can pivot around the joints, and have wire guides through which wires are passed. In each of the articular rings, the wire guides are equally and oppositely distanced from an axis of the articular ring in a diametral direction.
When one of the wires is pulled and the other released through an operation mechanism 108 of the controller 107, the flexible section 105 curves. At this time, the front end 101 curves along an arc of large radius whose center is positioned close to the flexible tube 103, so that the front end 101 may hit a celomic site to stop curving or to injure an internal wall of the celomic site.
To deal with this problem, Japanese Utility Model Publication No. 60-41206 proposes a flexible section 105 of FIG. 2. The flexible section 105 comprises articular rings 109 each having a fitting plate 111 extending along a diameter of the articular ring. The fitting plate 111 has a pair of wire guides 113. Diametral distances between the wire guides 113 of the respective articular rings 109 become larger from a rear end of the flexible section 105 toward a front end 101.
FIG. 3 shows the articular ring 109 positioned close to the front end 101, and FIG. 4 the articular ring 109 positioned away from the front end 101.
When wires 115 passing through the wire guides 113 move, the articular ring 109 in the vicinity of the front end 101 receives a large angular moment, so that the flexible section 105 may curve from the front end portion at a small radius of curvature.
FIG. 5 is a sectional view showing a flexible section 105 disclosed in Japanese Laid-Open Patent Publication No. 62-281918. This flexible section 105 has articular rings 119 each having wire guides 123. The articular rings 119 are connected to one another through joints 121.
FIG. 6 is a cross-sectional view showing the articular ring 119 positioned close to a front end 10 of FIG. 5. In this articular ring 119, the wire guides 123 are farthest from the joints 121 of this articular ring compared with those in the other articular rings 119. The wire guides 123 of the respective articular rings 119 gradually approach their corresponding joints 121 from the front end 10 toward a rear end of the flexible section 105 as showing in FIGS. 5 to 8.
When wires 125 passing through the wire guides 123 move, the articular ring 119 in the vicinity of the front end 10 receives a larger angular moment than the articular ring 119 in the vicinity of the rear end, so that the flexible section 105 may curve from the front end side at a small radius of curvature.
In these conventional flexible sections 105, a distance between any adjacent two joints 106 or 121 is identical, so that the conventional flexible sections 105 may provide only a few variations of curved shapes.
Namely, the conventional flexible sections cannot provide a sufficiently small radius of curvature at front ends thereof, and cannot gradually curve from rear ends thereof.
According to the Japanese Utility Model Publication No. 60-41206, the flexible section 105 has the fitting plates 111 each extending along the whole diameter of the articular ring 109. The fitting plates 111 narrow the insides of the articular rings 109 so that the wires 115, observation and illumination fibers, and various tubes may not easily be positioned inside the articular rings 109, thereby reducing a filling ratio of the articular rings 109 and complicating the articular rings 109.
According to the Japanese Laid-Open Patent Publication No. 62-281918, the wire guides 123 gradually approach the joints 121 in the articular rings 119 from the front end side toward the rear end side of the flexible section 105. Namely, the wire guides 123 and wires 125 are not arranged straight but twisted in a longitudinal direction. The wires 125, therefore, must be strongly pulled to curve the articular rings 119 because this arrangement consumes an unnecessary force in bending. Compared with a straight arrangement of wires and wire guides, the twisted arrangement is not efficient in bending the flexible section 105.
Namely, the spirally arranged wire guides 123 inevitably increase a force to be applied to the wires 125 in a bending operation as well as frictional force between the wires 125 and the wire guides 123, thereby shortening their service lives.
Due to the twisted arrangement of the wire guides 125, not only the wires 125 but also the observation and illumination fibers and various tubes which are observation and operation means and disposed inside the articular rings 119 change their diametral positions along a longitudinal axis by sliding spirally during the curving operation. This increases an apparent flexural rigidity of the flexible section 105, thereby increasing a bending force and a wire operating force to relatively easily break the fibers and tubes.
In addition, arranging the wire guides 123 successively at spiral positions in the articular rings 119 increases the number of processes, time and labor in manufacturing the endoscope.
In this way, the flexible sections of conventional endoscopes comprise articular rings of identical size, and wire guides disposed at regular positions so that they may provide only a few variations of final curved shapes. In addition, the conventional flexible sections require a large force for operating the wires in curving the flexible sections, thereby deteriorating operability of the endoscopes and shortening service lives of the wires and wire guides due to abrasion.